Diffusion pump



Patented Sept. 2, 1924.

UNITED STATES FREDERICK S. MQCULLOUGH, 0F WILKINSBURG, PENNSYLVANIA.

DIFFUSION PUMP.

Application filed December 11, 1922. Serial No. 606,346.

To all whom it may concern Be it known that I, Fnnnmucx S. MoCUL- nouorna citizen of the United States, and a resident of Vilkinsburg, in the count of Allegheny and State of Pennsylvania, ave invented a new and useful Improvement in Difiusion Pumps, of which the following is a specification.

My invention relates to vacuum pumps, having particular relation to difi'usion pumps of the type wherein a blast of hot vapor is projected from a nozzle, to draw gas from a vessel to be exhausted, partially by an injector action and partially by the diffusion of the gas to be pumped, into the vapor blast.

The principal object of my invention is to provide a vacuum pump of the class described which is characterized b the ex tremely high degree of vacuum 0 tainable; by the absence of complicated adjustments and corrections during operation; b the increased speed of evacuation obtaina- 1e; and by cheapness of construction and-manufacture.

More specifically, another object of my invention is to provide a boiler of an improved type for use with such diffusion pumps, whereby the above-mentioned desirable results may be obtained.

A further object of my invention is to provide means for increasing the velocity of the hot vapor blast by an arc, whereby the effectiveness of the pump may be greatly increased.

According to my invention, I provide a difi'usionpump comprising a boiler in the form of a transformer winding, 9. condensing chamber having spaced inlet and outlet passages for the passage of the gas to be exhausted, and additional inlet and outlet passages for introducing a hot vapor blast to the condensing chamber from said boiler and for returnin the condensate from the condensing chain er to said boiler.

With these and other objects and applications in mind, my invention further consists in the details of construction and operation hereinafter described and claimed and illustrated in the accompanying drawing, wherein:

Figure 1 is a front elevational view of one form of difi'usion, pump embodying my invention, certain portions'being shown in longitudinal section, and

Fig. 2 is a side elevational view of the structure shown in Fig. 1.

In the illustrated form of embodiment of my invention shown in the drawing, a boiler 1, of a diffusion pum 2, comprises a glass tube ,3, which is bent into the form of a helix, the end portions 4 and 5 of which extend vertically upward and awa from the horizontal axis of the helix. he curved portions of the tubing may be filled with a .readily vaporizable conducting material 6,

as mercury, whereby the helix may serve as a secondary winding 7 of a a transformer, the primary winding 9 of which is adapted to be connected to a source of high-frequency alternating current (not shown). Hence, the end portions 4 and 5 of the boiler 1 constitute the terminals of the secondary winding 7 which is formed by the tubular member 3.

The vapor arising from one of the end portions of the boiler 1 for example, 4 when the same is energize as hereinafter explained, may be carried by a tubular member 11 to a nozzle 12 and projected through the same into the top portion 13 of a condensing chamber 14, the latter comp-rising a vertical tubular member 15. Immediately above the entrance of the nozzle 12 into the condensing chamber 14, an entrance chamber 16 is provided for an inlet tube 17 which is connected to a vessel (not shown) to be evacuated. The lower portion of the pump 2 is provided with an outlet tube 18 for the removal of the gases drawn in through the inlet tube 17, as hereinafter more fully explained.

An annular casing 19 surrounds the condensing chamber 14 and it is sealed to the opposite ends of the tubular member 15 which constitutes said chamber. A; cooling fluid for condensing the vapor blast in the condensing chamber 14 is supplied to the chamber formed by the casing 19 through a passage 21 which opens into said casing 19 just above the point of entrance of the nozzle 12 into the condensing chamber 14. The cooling fluid leaves the casing 19 through a passage 22 leading from the lower portion thereof.

The condensed vapor, which accumulates in the lower portion of the condensing chamber 14, is led back to the remaining terminal portion 5 of the boiler 1 through a tubular member 23. This member is provided with an opening 24 for the outlet tube l8, whereby the gases drawn in through the tube 17 may be exhausted from the pump. The condensing chamber 1 1 is preferably so positioned with respect to. the two end-portions 4 and 5 that the cooling liquid traversing said condenser maintains vaporizable liquid in the end portion 5, of the boiler 1 in a substantially non-vaporizable state without impeding the vaporization of the mercury in the other end portion 4:. The result just mentioned is very desirable, since, if the mercury were permitted to vaporize in the end portion 5, the efficiency of the pump would be greatly decreased as will be readily understood by those skilled in the art.

In operation, when alternating-current energy is supplied to the primary winding 9 of the transformer 8, eddy currents are established in the mercury of the boiler 1, heating the same and finally resulting in the establishment of a hot-vapor arc blast extending from end portion 4 of the boiler 1. The blast is carried by the tubular member 11 to the nozzle 12 and it is then projected downwardly into the condensing chamber 14. As the vapor are blast enters the condensing chamber 14, the gas to be operated upon is drawn through the inlet tube 17 partially by an injector action and partially by diffusion. The vapor arc blast, upon entry into the condensing chamber 14, is condensed on the cooled walls of the tubular member 15, and the condensate falls into the end portion 5 of the boiler 1 by way of the tube 23. The gas, which is drawn into the condensing chamber 14: by the action of the pump, exhausts through the outlet passage 18 to the atmosphere or to a so-called roughing pump (not shown), as is customary in the art.

When the boiler is energized by the passing of electrical currents through the primary winding of the transformer, an additional effect is obtained which is not found in any of the devices prior to my invention, viz., the establishment of an induced alternating voltage in the transformer winding 7 formed by the helices of the boiler 1, having a novel effect as follows.

The external circuit of the secondary transformer winding 7 is completed through the path provided by the mercury blast in the tubular member 11 and the path provided by the condensed mercury vapor in the condens ing chamber 14, and in the return tube 23. Hence, currents are established in the external circuit of the secondary winding, and it has been observed that such currents main 'tain the arc blast in-a high state of'fiuidity,

thereby increasing the etficiency and the speed of operation of the pump, since the efficiency depends upon the smallness of the mercury particles passing through the noztrical current discharge.

zle. Furthermore, the operation of the induced voltage in the secondary winding is to materially increase the velocity of the vapor arc blast, and hence the eliiciency of the pump.

Though I have shown only one modification of my invention, for the purpose of describing the same and illustrating its principles of construction and of operation, it is apparent that the various changes and modifications may be made therein without departing from the spirit of my invention. I desire, therefore, that only such limitations shall be imposed thereon as are indicated by the appended claims or demanded by the prior art.

I claim as my invention: a

1. The method of increasing the velocity of a vapor arc blast at the entry of a condensation chamber of a vacuum pump, which consists in establishing a voltage drop in said blast.

2. A vacuum pump comprising a condensing chamber, means for introducing a vapor blast therein and means for establishing a potential drop in said vapor blast.

3. In combination, means for establishing a vapor arc blast, a condensing chamber for receiving said blast and electrical means for increasing the velocity of said blast.

4. In combination, means for establishing a vapor arc blast, a condenser chamber for receiving said blast, means for increasing the velocity of said blast .and for maintaining the material thereof in a vaporized condition.

5. In combination, means for establishing a vapor arc blast, a condenser chamber for receiving said blast, and electrical means for increasing the velocity of said blast and for maintaining the material thereof in a vaporized condition.

6. In a vacuum pump, the combination with means for establishing a vapor are blast, of means for condensing said blast, whereby a vacuum is produced, and means for establishing in said vapor blast an elec- 7 In a condensation pump, a boiler of insulating tubing, the contents of said boiler constituting the secondary 'winding of a transformer, the contents of the end portions of said boiler serving as the terminals of said secondary winding.

8. In a vacuum pump of the condensation type, a boiler forming the secondary winding of a transformer, the terminals of said winding being closed through a condensation chamber.

- 9. In a vacuum pump, a boiler so arranged as to constitute the secondary winding ol? a.

transformer, a condensing chamber having inlet and outlet portions for the entrance and exit of the gas to be operated on. means for connecting said condensing chamber to points of different potential on said secondary winding, and means for establishing a hot-vapor blast extending from said boiler into said condensing chamber.

10. In a diffusion pump, a boiler constituting the secondary winding of a transformer, said boiler having end portions serving as terminals for said secondary winding, a condensing chamber having spaced inlet and outlet passages for the gas to be operated on, means for projecting a hot-vapor blast from one of said end portions into said condensing chamber intermediate said passages.

11. In a vacuum pump, the combination with a boiler in the form of a transformer winding and provided with spaced terminal portions, of a condensing chamber having spaced inlet and outlet passages for a gas to be operated on, said condensing chamber having additional inlet and outlet passages connected, respectively, with said terminal portions.

12. In a diffusion pump, the combination Wth a boiler in the form of a transformer winding and provided with spaced terminal portions, of a condensing chamber having spaced inlet and outlet passages for a gas to be operated on, means for connecting one of said terminal portions with a point in said condensing chamber intermediate said passages, whereby a vapor blast may be introduced in said chamber, and means for con ducting away the'condensed vapor.

13. In a diffusion pump, the combination with a boiler in the form of a transformer winding and provided with spaced terminal portions, of a condensing chamber having spaced inlet and outlet passages for a gas to be operated on, additional inlet and outlet passages, said additional inlet-passages extending from one of said spaced terminal portions 'to a point in said condensing chamber intermediate said first-mentioned passages and serving to provide a passage for a vapor blast, said additional outlet assage extending to the remaining end portion and serving to conduct away the vapor condensed in said chamber.

14. In a diffusion pump, the combination with a boiler in the form of a transformer winding and provided with spaced terminal portions, of means for heating said boiler, a

condensing chamber having spaced inlet and outlet passages for a gas to be operated on, a nozzle disposed within said condensing chamber intermediate said passages and extending to one of said terminal portions, and means for conducting the condensed vapor in said chamber to the remaining terminal portion, said condensing chamber being so disposed as to unbalance the relative temperatures of said terminal portions.

15. In a diffusion pump, the combination with a boiler in the form of a transformer winding and provided with spaced terminal portions, of means constituting the primary winding of a transformer of which said boiler is the secondary, whereby a potential may be established across said terminal portions, a condensing chamber having spaced inlet and outlet passages for a gas to be operated on, a nozzle disposed within said condensing chamber intermediate said passages and extending to one of said terminal portions, and means for conducting condensed vapor in said chamber to the remaining terminal portion, said condensing chamber being so disposed as to prevent substantially any vaporization at said last-mentioned terminal portion.

16. In a diffusion pump, the combination with a boiler containing a vaporizable liquid and constructed in the form of a transformer winding provided with end portions, of means constituting the primary winding of a transformer of which said boiler is the secondary, whereby a potential may be established across said terminal portions and said liquid heated to the vaporization point, a condensing chamber having spaced inlet and outlet passages for a gas to be operated on, a nozzle disposed within said condensing chamber intermediate said passages and extending to one of said terminal portions, and means for conducting condensed vapor in said chamber to the remaining terminal portion, said condensing chamber being so disposed as to prevent substantially any vaporization at said last-mentioned terminal portion.

In testimony whereof, I have hereunto subscribed my name this 7th day of December 1922.

FREDERICK S. MCCULLOUGH. 

